MTU method has always worked wonders
Swear if they patch that too I'm fckn done with this game
Maximum Transmission Unit size. It's what determines datagram size of a network packet, and is part of the underlying IPv4 and is determiend by the RFCs that alow the Internet to work.
Depending on the method of connectivity, MTUs are set. If they're too big they'll fragment and cause latency and other issues, or in teh case of what people do here, if they're purposedly forced too small they'll come across as fragmented (because the Internet expects an MTU of 1500) and thus due to the poor performance you'll get dropped into a solo lobby.
The general problem is since you're forcing a Rockstar to see your intentionally too small datagrams as fragmented, and thus segregating you into a solo session for poor performance, it's hard for others to join you. You've physically, manually, handicapped your network link and the game can't actually link more people into a meshed session because you're MTU is too low.
Other interesting things I've learned: If you pull(or shutdown) the eth port (wireless, as well) on your PS4 it cuts you off instantly, but if you jsut f*ck with it beyond the next hop (ie, I can pull the eth on the uplinked port on my switch before it hits router or bridge) it'll let you carry on for about 10 seconds before it then says "no network found." Ergo, pulling said uplink a couple times in a row for 10 seconds is enough to force a solo section the same way as using lag switch.
Easy for me to do. Probably not so easy for others, but it's anotehr thing to add to the pile of knowledge.